372 



THE MUSCULATURE 



dorsi, teres major, and subscapularis muscles behind; by the subscapularis muscle toward the 

 joint; and by the serratus anterior (magnus) toward the thoracic wall. In the groove between 

 the coraco-brachiahs and the subscapularis and tendons of the latissimus dorsi and teres major 

 muscles run the main nerves and vessels of the arm. These are surrounded by a considerable 

 amount of connective tissue in which numerous blood- and lymph-vessels, lymph-nodes, 

 nerves, and masses of fat are embedded. 



Fig. 360. — The Pectoralis Major and Deltoid. 



Sterno-cleido- 

 mastoid 



Aponeurosis of external oblique 



External intercostal 



Over this connective tissue the fascia covering the musculature of the neighbouring portion 

 of the shoulder and thorax is continued into the fascia covering the musculature of the medial 

 side of the arm. Thus the fascia covering the pectoralis minor, the cora(!0-clavicular fascia, 

 strengthened by a reflection of the fascial investment of the pectoralis major and deltoid muscles- 

 is continued across the ventral margin of the arm-pit into the fascia which covers the coraco- 

 brachialis and biceps muscles in the arm. Similarly, dorsally, the fascia covering the latissimus 

 dorsi and teres major is continued over the arm-pit into that covering the long head of the triceps 

 in the arm. The ventral is connected with the dorsal fascia by a thin membrane which is 

 adherent to the connective tissue filling the axillary space and to the subcutaneous tissue. 

 On the trunk this meml)rane, the fascia axillaris, becomes fused below the axillary fossa with 

 the fascia of the serratus anterior (magnus). In the arm it becomes fused with the fascia over 

 the biceps muscle. Owing to its adherence to the skin and the connective tissue of the axillary 

 fossa, investigators have dissected out and figured the axillary fascia in different ways. 



MUSCLES 



Tlie pectoralis major (fig. 300). — Origin. — (1) From the medial half of the clavicle; (2) 

 from tlie side and front of the sternum as far as the sixth costal cartilage; (3) from the front of 

 the cartilages of tlic second to the sixth ribs; and (4) from the upper i)art of tlie aponevn'osis of 

 the external oblitjut! where this extends over the rectus abdominis imiscle. The costal origin 

 may in part take place from the osseous extremities of tlie sixth and seventh ribs. 



Jnncrlion. — (Jrest of the greater tiilierclc (outer lip of the bicipital groove) of the humerus 

 from the tubercle to the insertion of the deltoid (fig. 174). Some of the tendon fibres are also 

 continued into the tendon of the deltoid and adjacent fibrous septa and into the fibrous lining 

 of the intertubercular sulcus. 



Slructvrc. — '^I'he muscle is divisible into a series of overlapping layers spread out like a fan. 

 Of these, the clavicular portion forms tli(! most cranial and superficial layer, and the portion of 

 the mu.sde springing from the ajxinenrosis of the external oblifpie, the most caudal and deepest 

 layer. This last layer has a special tendon, while the other layers arc inserted into a combined 



